The characterization of the high molecular weight form of the nerve growth factor, 7S NGF, in terms of its chemical, physical and biological properties will be continued. This will include determination of the subunit composition of 7S NGF, a more detailed definition of its dissociation equilibria as well as the identification of the number of peptide chains within each subunit and of the chemical differences between the individual subunits. 7S NGF and its specific NGF subunit, the beta subunit, will be compared with the NGF proteins from snake venom and other preparations from the mouse submaxillary gland. To determine whether 7S NGF is just a package of three types of protein with different and unrelated activities or whether the complex itself has physiological significance, experiments involving cross linking of subunits, inhibition of the enzymatic activity of the gamma subunit or modification of one or more subunits will be carried out. I125-labelled 7S NGF will be used to define the cellular interactions of the complex and its subunits. Further studies on the variation in brain membrane proteins during development of the mouse will be made particularly with respect to synaptic membranes. Comparison between inbred strains of mice, neurological mutant strains and other rodents showing different patterns of maturation will be made.